The processing capacity available at the highest levels of the central nervous system is far less than the amount of information carried by the sensory pathways at any instant in time. Selective attention allows the brain to cope with this sensory overload by focusing on a subset of the available information. Although the relationship between selective attention and behavioral performance has been studied extensively, the physiological mechanism is virtually unknown. The long-term goal of this research is to discover the neural circuitry and physiological processes that underlie selective attention. New knowledge about this mechanism is likely to have a major impact on the understanding of psychiatric and neurological disorders that result in attention deficits. The proposed research will test important aspects of a model that attributes visual attention to an interaction between the posterior parietal areas of the cerebral cortex and the pulvinar nucleus of the thalamus. The role of the parietal cortex in this model is to encode information about the spatial location of salient stimuli in multiple stimulus scenes. The spatial information is then relayed to the pulvinar which in turn selectively gates information (the focus of attention) from middle-level feature maps to the higher-level visual areas responsible for object recognition. Reciprocal the interaction between the parietal cortex and pulvinar could account for the periods of enhancement followed by inhibition of return typically observed in behavioral experiments. This model will be tested by seeking correlation between of neuronal activity recorded in the parietal cortex and pulvinar of awake monkeys with measures of their behavioral performance during visual attention tasks. The first specific aim is to correlate the magnitude and time course of activity in parietal neurons with changes in reaction times associated with cued attention tasks. A second specific aim is to identify the coordinate system used by the parietal cortex to encode spatial information by quantifying the effects of changes in eye position on neuronal responses during attention tasks. The third specific aim is to produce a dynamic model of neuronal responses that will display a continuous temporal pattern of activity in the parietal cortex during the redirection of attention from one location to another. The fourth specific aim of this proposal is to correlate neuronal activity in the pulvinar with that observed in the parietal cortex with the goal of determining whether the properties of pulvinar neurons are consistent with those predicted by visual attention models.